Ferdinando Taddei - Academia.edu (original) (raw)
Papers by Ferdinando Taddei
Journal of Molecular Structure, 1997
The 1H, 13C and (partly) the 15N NMR spectra of a number of 5,5-disubstituted hydantoins were rec... more The 1H, 13C and (partly) the 15N NMR spectra of a number of 5,5-disubstituted hydantoins were recorded and assigned by the various methods of 1D and 2D NMR spectroscopy. Employing the NMR parameters, thus obtained, the NOEs between the different protons within the molecules and the results of accompanying semiempirical (AM1 and PM3, respectively) and ab initio (3-21G and, when
AIP Conference Proceedings, 2007
The main goal of this communication is to show the utility of empirical approaches combined with ... more The main goal of this communication is to show the utility of empirical approaches combined with mathematical methods in the research regarding the molecular basis of biological chirality. Preparative results (enantiomeric excesses, e.e.) obtained in asymmetric autocatalysis with (AAC) and without (AES) chiral additive were analyzed. Statistical calculations show, that AES (absolute enantioselective synthesis) experiments yield two independent groups of
Advances in Heterocyclic Chemistry, 1987
ABSTRACT
Chemischer Informationsdienst, 1974
Journal of Molecular Structure: THEOCHEM, 2001
Journal of Heterocyclic Chemistry, 1970
Journal of Molecular Structure: THEOCHEM, 1994
J Chem Inf Model, 1998
The potential energy profile for a number of derivatives of benzene substituted with the SiH 3 , ... more The potential energy profile for a number of derivatives of benzene substituted with the SiH 3 , SiH 2 CH 3 , and CH 2 SiX 3 (X ) H, F, Cl, CH 3 ) groups was calculated at ab initio (HF/6-31G*//HF/6-31G*) level, and the energy barriers were estimated. The rotational barrier is low for the molecules with silicon directly bonded to the phenyl ring, but higher values are found for the CH 2 SiX 3 groups, which depend on X as well. The hyperconjugative effect of the substituents was estimated from the natural bond orbital (NBO) theory of donor acceptor properties: the SiH 2 CH 3 group was found to be electron-acceptor in character, and the CH 2 SiX 3 were found to be electron-donor groups. The rotational barrier of these molecules is mainly determined by hyperconjugation, steric effects being smaller than in the analogous carbon derivatives. The SisH and SisC bonds display an electron-acceptor character of similar magnitude when silicon is attached to the phenyl ring, but the SisC bond has a prevailing donor character when carbon is bonded to the phenyl ring.
Journal of the Chemical Society, 1964
Journal of Molecular Structure: THEOCHEM, 2001
Internal rotational barriers around the exocyclic partial CvC double bond were calculated for a w... more Internal rotational barriers around the exocyclic partial CvC double bond were calculated for a wide group of heterocyclic derivatives as a function of the different structure of the heterocyclic ring and of the nature of heteroatoms, by means of MO abinitio theory. The rotational barriers refer to the two-fold potential energy, V 2 , obtained from single-determinant Hartree± Fock (HF) wave functions and at MP2/6-31G p //HF/6-31G p level of theory. The V 2 values seem to represent homogeneously the rotational barrier in substituted ethylenes with varying polar character of the CvC bond, ranging from unpolarized ethylene to molecules having a marked push±pull character, and thus allow the effect of substituents on the height of the barrier to be compared. Sets of parameters quantifying the heteroatom effect of constantly modulating the barrier in the different heterocyclic rings were extracted, and two heteroatoms were found to have an additive effect when acting in the same ring. The difference between the V 2 values and the rotational barriers calculated from the HF energy of the perpendicular conformation is discussed in the light of a qualitative approach based on calculated contributions of singlet excited states to the electronic con®guration of the perpendicular conformation. q
Journal of Molecular Structure: THEOCHEM, 2005
The conformational equilibria of the cis/trans isomers of some 1,4-di-substituted cyclohexanes (X... more The conformational equilibria of the cis/trans isomers of some 1,4-di-substituted cyclohexanes (XZOH, OMe, Me, OCOCH 3 , OCOC(CH 3 ) 3 , OCOCCl 3 , OCOCF 3 ) were calculated at several levels of theory; the best correlation between calculated and experimentally available DG 0 s refers to the MP2/6-311CG*//MP2/6-311G* results. In addition, the hyperconjugative effect of the substituents was studied with the NBO options included in the package; a number of interactions between filled NBOs and antibonding orbitals could be considered as most representative for delocalization along the molecules studied. The effect of the substituents on the molecular geometry of the substituted cyclohexanes as well as the partitioning of both hyperconjugative and steric substituent effects on the present conformational equilibria is critically evaluated. Our model [E. Kleinpeter, F. Taddei, J. Mol. Struct. (THEOCHEM) 683 29] for interpreting the relative stability of conformers of substituted cyclohexanes could be further verified and its reliability assessed. q
Journal of the Chemical Society Perkin Transactions Ii, 1991
Magn Reson Chem, 1971
... shift of ortho positions and of the carbon atoms directly bonded to the substituents also see... more ... shift of ortho positions and of the carbon atoms directly bonded to the substituents also seems to be mainly determined by changes in electron density at the carbon atoms. The total charge densities calculated here differ in absolute value from those of Bloor and Breen? ...
Molecular Physics, May 1, 1972
J Chem Soc Perkin Trans 2, 1973
... 1 JP Paolini and RK Robins, J. Heterocyclic Chem., 1965, 21, 63. 2 WW Paudler and H. L. Blewi... more ... 1 JP Paolini and RK Robins, J. Heterocyclic Chem., 1965, 21, 63. 2 WW Paudler and H. L. Blewitt, J . Org. Chem., 1966, 31, 3 WW Paudler and JE Kuder, J . Org. Chem., 1966, 31, 4 P. Guerret, R. Jacquier, and G. Maury, Bull. SOC. chim. 1295. 809. France, 1972, 3503. ...
Cheminform, May 7, 1991
AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance th... more AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.
Journal of the American Chemical Society, 2003
The electron transfer (ET) to a series of para-substituted diaryl disulfides, having the general ... more The electron transfer (ET) to a series of para-substituted diaryl disulfides, having the general formula (X-C(6)H(4)S-)(2), has been studied. The X groups were selected as to have a comprehensive variation of the substituent effect, being X = NH(2), MeO, H, F, Cl, CO(2)Et, CN, and NO(2). The reduction was carried out experimentally, using N,N-dimethylformamide as the solvent, and by molecular orbital (MO) ab initio calculations. The ET was studied heterogeneously, by voltammetric reduction and convolution analysis, and homogeneously, by using electrogenerated radical anions as the solution electron donors. The reduction is dissociative, leading to the cleavage of the S-S bond in a stepwise manner. Both experimental approaches led us to estimate the E degrees and the intrinsic barrier values for the formation of the radical anions. Comparison of the independently obtained results allowed obtaining, for the first time, a quantitative description of the correlation between heterogeneous and homogeneous rate constants of ETs associated with significant inner reorganization energy. The experimental outcome was fully supported by the theoretical calculations, which provided information about the disulfide lowest unoccupied MOs (LUMOs) and singly occupied MO (SOMO), the bond dissociation energies, and the most significant structural modifications associated with radical anion formation. With disulfides bearing electron-donating or mildly electron-withdrawing groups, the inner reorganization is particularly large, which reflects the significant stretching of the S-S bond experienced by the molecule upon ET. The process entails formation of loose radical anion species in which the SOMO is heavily localized, as the LUMO, onto the frangible bond. As a consequence of the formation of these sigma-radical anions, the S-S bond energy of the latter is rather small and the cleavage rate constant is very large. With electron-withdrawing groups, the extent of delocalization of the SOMO onto the aryl system increases, leading to a decrease of the reorganization energy for radical anion formation. Interestingly, while the LUMO now has pi character, the actual reduction intermediate (and thus the SOMO) is still a sigma-type radical anion. With the nitro-substituted disulfide, very limited inner reorganization is required and a pi-radical anion initially forms. A nondissociative type intramolecular ET then ensues, leading to the formation of a new radical anion whose antibonding orbital has similar features as those of the SOMO of the other diaryl disulfides. Therefore, independently of the substituent, the actual S-S bond cleavage occurs in a quite similar way along the series investigated. The S-S bond cleavage rate, however, tends to decrease as the Hammett sigma increases, which would be in keeping with an increase of both the electronic and solvent reorganization energies.
Journal of the Chemical Society Perkin Transactions Ii, 1987
ABSTRACT
Can J Chem, 1995
ABSTRACT The crystal structures of the title compounds were determined by single crystal X-ray di... more ABSTRACT The crystal structures of the title compounds were determined by single crystal X-ray diffraction techniques. The molecule of the Z isomer, which crystallizes in the monoclinic space group C2/c with Z = 4 in a cell of dimensions a = 14.891 (2), b = 10.780(2), c = 8.769(1) Å, β = 97.47(2)°, V = 1395.7(7) Å3 has crystallographic twofold symmetry. The E form crystallizes in the orthorhombic space group Pbca with a = 11.730(1), b = 6.932(1), c = 16.841(1) Å, V = 1369.4(2) Å3 and Z = 4. Its molecules have crystallographically dictated symmetry. In both isomers the phenyl rings are roughly perpendicular to the average ethylene plane. The atoms characterizing this plane show significant deviations from planarity in the Z isomer. Marked bond-angle distortions at the ethene carbons of both structures are observed. The 1H and 13C NMR spectra of the compounds were measured and, particularly in the case of the 1H chemical shifts, fall into two quite separate spectral regions. At low temperature, two conformational isomers, those with different relative orientation of the C—Cl bonds of the phenyl rings, are observed in the spectrum of each compound. Keywords: chlorostilbenes, overcrowded molecules. X-ray structure, conformations, NMR spectroscopy.
Journal of Molecular Structure, 1997
The 1H, 13C and (partly) the 15N NMR spectra of a number of 5,5-disubstituted hydantoins were rec... more The 1H, 13C and (partly) the 15N NMR spectra of a number of 5,5-disubstituted hydantoins were recorded and assigned by the various methods of 1D and 2D NMR spectroscopy. Employing the NMR parameters, thus obtained, the NOEs between the different protons within the molecules and the results of accompanying semiempirical (AM1 and PM3, respectively) and ab initio (3-21G and, when
AIP Conference Proceedings, 2007
The main goal of this communication is to show the utility of empirical approaches combined with ... more The main goal of this communication is to show the utility of empirical approaches combined with mathematical methods in the research regarding the molecular basis of biological chirality. Preparative results (enantiomeric excesses, e.e.) obtained in asymmetric autocatalysis with (AAC) and without (AES) chiral additive were analyzed. Statistical calculations show, that AES (absolute enantioselective synthesis) experiments yield two independent groups of
Advances in Heterocyclic Chemistry, 1987
ABSTRACT
Chemischer Informationsdienst, 1974
Journal of Molecular Structure: THEOCHEM, 2001
Journal of Heterocyclic Chemistry, 1970
Journal of Molecular Structure: THEOCHEM, 1994
J Chem Inf Model, 1998
The potential energy profile for a number of derivatives of benzene substituted with the SiH 3 , ... more The potential energy profile for a number of derivatives of benzene substituted with the SiH 3 , SiH 2 CH 3 , and CH 2 SiX 3 (X ) H, F, Cl, CH 3 ) groups was calculated at ab initio (HF/6-31G*//HF/6-31G*) level, and the energy barriers were estimated. The rotational barrier is low for the molecules with silicon directly bonded to the phenyl ring, but higher values are found for the CH 2 SiX 3 groups, which depend on X as well. The hyperconjugative effect of the substituents was estimated from the natural bond orbital (NBO) theory of donor acceptor properties: the SiH 2 CH 3 group was found to be electron-acceptor in character, and the CH 2 SiX 3 were found to be electron-donor groups. The rotational barrier of these molecules is mainly determined by hyperconjugation, steric effects being smaller than in the analogous carbon derivatives. The SisH and SisC bonds display an electron-acceptor character of similar magnitude when silicon is attached to the phenyl ring, but the SisC bond has a prevailing donor character when carbon is bonded to the phenyl ring.
Journal of the Chemical Society, 1964
Journal of Molecular Structure: THEOCHEM, 2001
Internal rotational barriers around the exocyclic partial CvC double bond were calculated for a w... more Internal rotational barriers around the exocyclic partial CvC double bond were calculated for a wide group of heterocyclic derivatives as a function of the different structure of the heterocyclic ring and of the nature of heteroatoms, by means of MO abinitio theory. The rotational barriers refer to the two-fold potential energy, V 2 , obtained from single-determinant Hartree± Fock (HF) wave functions and at MP2/6-31G p //HF/6-31G p level of theory. The V 2 values seem to represent homogeneously the rotational barrier in substituted ethylenes with varying polar character of the CvC bond, ranging from unpolarized ethylene to molecules having a marked push±pull character, and thus allow the effect of substituents on the height of the barrier to be compared. Sets of parameters quantifying the heteroatom effect of constantly modulating the barrier in the different heterocyclic rings were extracted, and two heteroatoms were found to have an additive effect when acting in the same ring. The difference between the V 2 values and the rotational barriers calculated from the HF energy of the perpendicular conformation is discussed in the light of a qualitative approach based on calculated contributions of singlet excited states to the electronic con®guration of the perpendicular conformation. q
Journal of Molecular Structure: THEOCHEM, 2005
The conformational equilibria of the cis/trans isomers of some 1,4-di-substituted cyclohexanes (X... more The conformational equilibria of the cis/trans isomers of some 1,4-di-substituted cyclohexanes (XZOH, OMe, Me, OCOCH 3 , OCOC(CH 3 ) 3 , OCOCCl 3 , OCOCF 3 ) were calculated at several levels of theory; the best correlation between calculated and experimentally available DG 0 s refers to the MP2/6-311CG*//MP2/6-311G* results. In addition, the hyperconjugative effect of the substituents was studied with the NBO options included in the package; a number of interactions between filled NBOs and antibonding orbitals could be considered as most representative for delocalization along the molecules studied. The effect of the substituents on the molecular geometry of the substituted cyclohexanes as well as the partitioning of both hyperconjugative and steric substituent effects on the present conformational equilibria is critically evaluated. Our model [E. Kleinpeter, F. Taddei, J. Mol. Struct. (THEOCHEM) 683 29] for interpreting the relative stability of conformers of substituted cyclohexanes could be further verified and its reliability assessed. q
Journal of the Chemical Society Perkin Transactions Ii, 1991
Magn Reson Chem, 1971
... shift of ortho positions and of the carbon atoms directly bonded to the substituents also see... more ... shift of ortho positions and of the carbon atoms directly bonded to the substituents also seems to be mainly determined by changes in electron density at the carbon atoms. The total charge densities calculated here differ in absolute value from those of Bloor and Breen? ...
Molecular Physics, May 1, 1972
J Chem Soc Perkin Trans 2, 1973
... 1 JP Paolini and RK Robins, J. Heterocyclic Chem., 1965, 21, 63. 2 WW Paudler and H. L. Blewi... more ... 1 JP Paolini and RK Robins, J. Heterocyclic Chem., 1965, 21, 63. 2 WW Paudler and H. L. Blewitt, J . Org. Chem., 1966, 31, 3 WW Paudler and JE Kuder, J . Org. Chem., 1966, 31, 4 P. Guerret, R. Jacquier, and G. Maury, Bull. SOC. chim. 1295. 809. France, 1972, 3503. ...
Cheminform, May 7, 1991
AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance th... more AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.
Journal of the American Chemical Society, 2003
The electron transfer (ET) to a series of para-substituted diaryl disulfides, having the general ... more The electron transfer (ET) to a series of para-substituted diaryl disulfides, having the general formula (X-C(6)H(4)S-)(2), has been studied. The X groups were selected as to have a comprehensive variation of the substituent effect, being X = NH(2), MeO, H, F, Cl, CO(2)Et, CN, and NO(2). The reduction was carried out experimentally, using N,N-dimethylformamide as the solvent, and by molecular orbital (MO) ab initio calculations. The ET was studied heterogeneously, by voltammetric reduction and convolution analysis, and homogeneously, by using electrogenerated radical anions as the solution electron donors. The reduction is dissociative, leading to the cleavage of the S-S bond in a stepwise manner. Both experimental approaches led us to estimate the E degrees and the intrinsic barrier values for the formation of the radical anions. Comparison of the independently obtained results allowed obtaining, for the first time, a quantitative description of the correlation between heterogeneous and homogeneous rate constants of ETs associated with significant inner reorganization energy. The experimental outcome was fully supported by the theoretical calculations, which provided information about the disulfide lowest unoccupied MOs (LUMOs) and singly occupied MO (SOMO), the bond dissociation energies, and the most significant structural modifications associated with radical anion formation. With disulfides bearing electron-donating or mildly electron-withdrawing groups, the inner reorganization is particularly large, which reflects the significant stretching of the S-S bond experienced by the molecule upon ET. The process entails formation of loose radical anion species in which the SOMO is heavily localized, as the LUMO, onto the frangible bond. As a consequence of the formation of these sigma-radical anions, the S-S bond energy of the latter is rather small and the cleavage rate constant is very large. With electron-withdrawing groups, the extent of delocalization of the SOMO onto the aryl system increases, leading to a decrease of the reorganization energy for radical anion formation. Interestingly, while the LUMO now has pi character, the actual reduction intermediate (and thus the SOMO) is still a sigma-type radical anion. With the nitro-substituted disulfide, very limited inner reorganization is required and a pi-radical anion initially forms. A nondissociative type intramolecular ET then ensues, leading to the formation of a new radical anion whose antibonding orbital has similar features as those of the SOMO of the other diaryl disulfides. Therefore, independently of the substituent, the actual S-S bond cleavage occurs in a quite similar way along the series investigated. The S-S bond cleavage rate, however, tends to decrease as the Hammett sigma increases, which would be in keeping with an increase of both the electronic and solvent reorganization energies.
Journal of the Chemical Society Perkin Transactions Ii, 1987
ABSTRACT
Can J Chem, 1995
ABSTRACT The crystal structures of the title compounds were determined by single crystal X-ray di... more ABSTRACT The crystal structures of the title compounds were determined by single crystal X-ray diffraction techniques. The molecule of the Z isomer, which crystallizes in the monoclinic space group C2/c with Z = 4 in a cell of dimensions a = 14.891 (2), b = 10.780(2), c = 8.769(1) Å, β = 97.47(2)°, V = 1395.7(7) Å3 has crystallographic twofold symmetry. The E form crystallizes in the orthorhombic space group Pbca with a = 11.730(1), b = 6.932(1), c = 16.841(1) Å, V = 1369.4(2) Å3 and Z = 4. Its molecules have crystallographically dictated symmetry. In both isomers the phenyl rings are roughly perpendicular to the average ethylene plane. The atoms characterizing this plane show significant deviations from planarity in the Z isomer. Marked bond-angle distortions at the ethene carbons of both structures are observed. The 1H and 13C NMR spectra of the compounds were measured and, particularly in the case of the 1H chemical shifts, fall into two quite separate spectral regions. At low temperature, two conformational isomers, those with different relative orientation of the C—Cl bonds of the phenyl rings, are observed in the spectrum of each compound. Keywords: chlorostilbenes, overcrowded molecules. X-ray structure, conformations, NMR spectroscopy.